The present invention is based on a method and a device for generating an error signal in a motor vehicle having a break actuating means that is actuatable by the driver and through which a brake system is actuated, a detection means, through which actuation of the of the brake actuating means is detected, a gas pedal and a gas pedal position detector.
In today""s vehicles, brake lights are typically activated by actuating a brake pedal. To this end, the brake pedal actuated by the driver usually activates a brake switch. The position of this switch signals that the brake has been actuated. The signal from the brake switch can be used, in addition to activating the brake lights, for other vehicle systems such as engine, transmission control, and/or vehicle dynamics control. A defect in such a brake switch must be detected as early and as reliably as possible, since a defective brake switch may prevent different functions in the vehicle from being properly performed. Furthermore, there are functions that can be utilized or developed to further improve existing vehicle systems based on the assumption that the brake switch operates properly. A reliable brake switch signal, after all, indicates a driver""s intention to decelerate the vehicle and the signal is generated before a brake force is applied and before the vehicle begins to decelerate.
An object of the present invention is to generate an error signal indicating a defect in such a brake switch in a simple manner.
This object is achieved through the characterizing features of the independent claims.
As mentioned previously, the invention is based on a method and a device for generating an error signal in a motor vehicle. The vehicle has a drive engine and a brake actuating means actuated by the vehicle""s driver through which a brake system is activated. Detection means are provided through which the actuation of the brake actuating means is detected. Furthermore, the vehicle contains a gas pedal and a gas pedal position detector for determining the position of the gas pedal at any given time.
When the gas pedal is released, the time at which the gas pedal is released, a vehicle deceleration, and braking status are determined. The braking status represents the operating status of the brake actuating means. The elapsed time since gas pedal release is monitored, and an error signal is then generated as a function of the vehicle deceleration, the elapsed time and the braking status.
The present invention therefore includes monitoring the brake switch by monitoring elapsed time and vehicle deceleration subsequent to release of the gas pedal.
As mentioned previously, the brake actuating means may be provided in the form of a brake pedal and the detection means may be provided in the form of a brake switch through which actuation by means of the brake pedal is detected.
The error signal can represent the regular or irregular status of the detection means. A display means may be provided whose operating status changes in response to the error signal that has been generated.
In one embodiment of the present invention, the vehicle deceleration that has been determined is compared to a predetermined threshold deceleration value, and the time elapsed since gas pedal release is compared to a predetermined time quantity. The error signal is then generated to indicate an irregular status if: the vehicle deceleration that has been determined is greater than the predetermined threshold deceleration value, the time elapsed since gas pedal release is more than the predetermined time quantity, and the braking status indicates that no actuation of the brake actuating means has been detected.
The speeds of the vehicle wheels and/or the longitudinal acceleration of the vehicle are preferably measured in order to determine the vehicle deceleration. The longitudinal acceleration can be determined, for example, from the transmission output rotation speed or the wheel rotation speed by differentiation.
Furthermore, a signal representing the operating status of a clutch arranged in the power train of the vehicle may be taken into account in generating the error signal. For example, the error signal can be accounted for if the clutch becomes disengaged after gas pedal release.
Additional advantageous embodiments are presented in the dependent claims.